Dental trays are commonly used to apply medication to the teeth and/or gum tissue of patients. The movement of the tongue, muscles of the mouth and opposing dentition against the dental tray, however, create hydrodynamic forces that causes water or saliva and the medication to move. The primary movement is from the lingual to buccolabial side of the arch, and out over the gingival edge of the dental tray. A secondary movement is created along the length of the recess of the dental tray and out the distal ends of the tray. Consequently, the medication tends to be expelled from the tray and swallowed by the patient in a relatively short period of time.
U.S. Pat. No. 2,257,709 (Anderson) discloses a dental appliance that defines a closed chamber around the teeth. The dental appliance includes a plurality of fingers that create a massaging or rubbing action against the teeth. A cleansing preparation can be applied to the chamber so that it will be flushed in and out around the fingers to aid in the cleansing and massaging actions. A plunger action from the hydrodynamic forces in the mouth is thus created in the chamber, which forces the cleansing and treating material into and out of all cavities, spaces between the teeth, and even between the marginal edges of the gums and the teeth. Although the flaps on the dental appliance theoretically adhere to the gums, in practice, the plunger action disclosed in Anderson likely forces the cleansing preparation into the patient's mouth, where it is swallowed.
U.S. Pat. No. 3,527,219 (Greenberg) discloses a dental tray having a foam or open cell insert for carrying a medication. The hydrodynamic forces within the mouth compress the foam to create a pumping action that expels the medication from the dental tray.
U.S. Pat. No. 5,460,527 (Kittelsen) discloses a composite dental bleaching tray having a plurality of pockets on an inner surface to receive and hold a bleaching gel for bleaching teeth. Similarly, U.S. Pat. No. 5,234,342 (Fischer) discloses a method of making a dental tray with reservoirs formed opposite the teeth. The pockets of Kittelsen and the reservoirs of Fischer are both subject to the hydrodynamic forces of the mouth that cause the medication to be expelled from the dental tray.
Both the thickness and the flexibility of the material from which the tray is constructed are significant factors in the ability of the tray to resist hydrodynamic forces in the mouth. Dental trays made from material of about 2 millimeters (0.080 inches) to about 3.8 millimeters (0.150 inches) thick tend to be better at resisting hydrodynamic forces than dental trays made from thinner materials. On the other hand, dental professionals know that patients are more likely to wear a tray that is less obtrusive in the mouth. Dental trays made from sheet material of about 1 millimeter (0.040 inches) thick are far more comfortable to wear. Unfortunately, a dental tray of this thickness is more flexible and therefore tends to lack the mechanical stability to resist hydrodynamic forces.
When dental trays are used for teeth bleaching at home, the patient places an amount of a bleaching solution into each area of a dental tray for each tooth to be bleached. The tray is then placed in the mouth. Often, the bleaching solution is changed every 0.5 to 2.5 hours, and the dental tray is removed during meals. Sometimes a recommendation is made to wear the dental tray overnight. The efficacy of the bleaching procedure depends upon such factors as type and intensity of the stain, the bleaching agent contact time on the teeth, the amount of available active ingredient in the bleaching agent as well as patient acceptance and adherence to the procedure.
As can be appreciated, the cost for the teeth bleaching procedure is substantially less when the procedure is carried out at the patient's home rather than in the dental office, since the practitioner's time associated with the procedure is reduced. Moreover, patient discomfort associated with home-use tooth bleaching techniques both during and after treatment is reportedly less than that associated with conventional in-office bleaching.
Notwithstanding the foregoing advantages, there remain some important disadvantages to conventional home-use bleaching products and techniques. For example, the hydrodynamic forces in the mouth cause the volume of the bleaching agent in the tray to diminish rapidly over time, thereby decreasing the amount of active ingredient available for tooth bleaching. Test results show that after 30 minutes, less than 50% of the original quantity of bleaching agent was available for bleaching activity. After one hour, less than 25% of the bleaching agent was available for bleaching activity on the tooth surface (April 1997 Clinical Research Associates Newsletter). Thus, existing bleaching agents typically need to be replenished about every 15 to 30 minutes in order to maintain the most efficacious dosage of bleaching agent in contact with the tooth.
Unfortunately, the daytime schedules of many patients do not easily accommodate periodic, continuous replenishment of the bleaching agent. In addition, periodically replenishing the bleaching agent during the night is unrealistic for many patients. Since patient adherence to the procedure determines the ultimate success of the tooth bleaching treatment, the need to constantly replenish the dental bleaching agent is a major obstruction that limits the success of the treatment.